The marketing of unproven direct-to-consumer stem cell interventions is becoming widespread in Canada. There is little evidence supporting their use and they have been associated with a range of harms. Canada has been slower to act against clinics offering these interventions than other jurisdictions, including the United States. Here, we outline the regulatory and policy tools available in Canada to address this growing problem. Health Canada’s regulations governing cell therapies are complex, but recent statements make it clear that Health (...) Canada believes it has jurisdiction over many of the currently marketed stem cell interventions. Still, further regulatory clarity is needed from Health Canada, as are increased directed enforcement efforts on interventions that fall within their scope. The Competition Bureau, via the Competition Act, prohibits advertisers from making materially false or misleading promotional representations. The Competition Bureau could collaborate with the scientific community to analyze the claims of existing clinics in Canada, and impose sanctions upon those who breach the established standard. Professional regulators, including provincial colleges of physicians and surgeons, have considerable power over what products and services their members can offer. Every college of physicians in Canada requires, via policy and codes of ethics, that doctors maintain evidence-based practices. This requirement is incompatible with offering many unproven stem cell interventions. Litigation may be another tool, including the use of fraud, misrepresentation and/or negligence claims for failing to meet the required standard of care. Finally, political pressure on federal and provincial lawmakers could encourage changes to marketing, cell therapy and professional regulations that would allow a more comprehensive response. In sum, there are many existing tools that can be used to protect the public from unproven stem cell interventions. Increased bureaucratic will and grassroots efforts are needed in order to effect a positive policy response. (shrink)

The marketing of unproven direct-to-consumer stem cell interventions is becoming widespread in Canada. There is little evidence supporting their use and they have been associated with a range of harms. Canada has been slower to act against clinics offering these interventions than other jurisdictions, including the United States. Here, we outline the regulatory and policy tools available in Canada to address this growing problem. Health Canada’s regulations governing cell therapies are complex, but recent statements make it clear that Health (...) Canada believes it has jurisdiction over many of the currently marketed stem cell interventions. Still, further regulatory clarity is needed from Health Canada, as are increased directed enforcement efforts on interventions that fall within their scope. The Competition Bureau, via the Competition Act, prohibits advertisers from making materially false or misleading promotional representations. The Competition Bureau could collaborate with the scientific community to analyze the claims of existing clinics in Canada, and impose sanctions upon those who breach the established standard. Professional regulators, including provincial colleges of physicians and surgeons, have considerable power over what products and services their members can offer. Every college of physicians in Canada requires, via policy and codes of ethics, that doctors maintain evidence-based practices. This requirement is incompatible with offering many unproven stem cell interventions. Litigation may be another tool, including the use of fraud, misrepresentation and/or negligence claims for failing to meet the required standard of care. Finally, political pressure on federal and provincial lawmakers could encourage changes to marketing, cell therapy and professional regulations that would allow a more comprehensive response. In sum, there are many existing tools that can be used to protect the public from unproven stem cell interventions. Increased bureaucratic will and grassroots efforts are needed in order to effect a positive policy response. (shrink)

The regulation of stem cell research is an issue that has drawn much comment, criticism and even judicial arbitration in recent years. An emerging issue, addressed in this article, is how the fruits of that research-stem cell medicine-are likely to be regulated en route from lab to market. Taking account of the ethical, legal, social and safety issues raised by stem cell medicine and the goals of governance, the article explains the relevant regulatory instruments (e.g. the draft UK Stem (...) Cell Bank Code, the EU Directive on Human Tissue, the EU Directives on medical products and devices, and the Human Tissue Act 2004) and critically examines the framework they provide. (shrink)

Significant strides have been made in recent years towards understanding the molecular basis of cell cycle progression in the model bacterium Caulobacter crescentus. At the heart of cell cycle regulation is a multicomponent transcriptional feedback loop, governing the production of successive regulatory waves or pulses of at least three master regulatory proteins. These oscillating master regulators direct the execution of phase‐specific events and, importantly, through intrinsic genetic switches not only determine the length of a given phase, but also (...) provide the driving force that catapults the cell into the next stage of the cell cycle. The genetic switches act as fail safe mechanisms that prevent the cell cycle from relapsing and thus govern the ordered production and the periodicity of these regulatory waves. Here, we detail how the master regulators CtrA, GcrA and DnaA coordinate cell cycle progression and polar development in Caulobacter. BioEssays 28: 355–361, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

The stable differentiation of cells into other cell types typically involves dramatic reorganization of cellular structures and functions. This often includes remodeling of the cell cycle and the apparatus that controls it. Here we review our understanding of the role and regulation of cell cycle control elements during cell differentiation in the yeast, Saccharomyces cerevisiae. Although the process of differentiation may be more overtly obvious in metazoan organisms, those systems are by nature more difficult to study at a mechanistic (...) level. We consider the relatively well‐understood mechanisms by which mating‐type switching and the pheromone‐induced differentiation of gametes are coupled to the cell cycle as well as the more obscure mechanisms that govern the remodeling of the cell cycle during meiosis and filamentous growth. In some cases, the cell cycle is a primary stimulus for differentiation whereas, in other cases, the signals that promote differentiation alter the cell cycle. Thus, despite relative simplicity of these processes in yeast, the nature of the interplay between the cell cycle and differentiation is diverse. BioEssays 25:856–867, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

This article explores the plausibility of an argument against embryonic stem cell research based on what the regulations already say about research on pregnant women and fetuses. The center of the argument is the notion of vulnerability and whether such a concept is applicable to human embryos. It is argued that such an argument can be made plausible. The article concludes by responding to several important objections.

The pursuit of unproven stem cell-based interventions is an emerging issue that raises various concerns. Physicians play different roles in this market, many of which engage their legal, ethical and professional obligations. In Canada, physicians are members of a self-regulated profession and their professional regulatory bodies are responsible for regulating the practice of medicine and protecting the public interest. They also provide policy guidance to their members and discipline members for unprofessional conduct.

Cell and tissue-based products, such as autologous adult stem cells, are being prescribed by physicians across the world for diseases and illnesses that they have neither been approved for or been demonstrated as safe and effective in formal clinical trials. These doctors often form part of informal transnational networks that exploit differences and similarities in the regulatory systems across geographical contexts. In this paper, we examine the regulatory infrastructure of five geographically diverse but socio-economically comparable countries with (...) the aim of identifying similarities and differences in how these products are regulated and governed within clinical contexts. We find that while there are many subtle technical differences in how these regulations are implemented, they are sufficiently similar that it is difficult to explain why these practices appear more prevalent in some countries and not in others. We conclude with suggestions for how international governance frameworks might be improved to discourage the exploitation of vulnerable patient populations while enabling innovation in the clinical application of cellular therapies. (shrink)

Glycosylation refers to the co‐ and post‐translational modification of protein and lipids by monosaccharides or oligosaccharide chains. The surface of mammalian cells is decorated by a heterogeneous and highly complex array of protein and lipid linked glycan structures that vary significantly between different cell types, raising questions about their roles in development and disease pathogenesis. This review will begin by focusing on recent findings that define roles for cell surface protein and lipid glycosylation in pluripotent stem cells and (...) their functional impact during normal development. Then, we will describe how patient derived induced pluripotent stem cells are being used to model human diseases such as congenital disorders of glycosylation. Collectively, these studies indicate that cell surface glycans perform critical roles in human development and disease. (shrink)

The Human Fertilization and Embryology Authority policy on permitting ova provision for research purposes breaches good regulatory practice in being inconsistent, unaccountable and untargeted. This article will illustrate how these breaches have resulted in a policy which is unfair to ova providers who wish to contribute to stem cell research and undermines the intentions behind the policy's very inception. (This article is based on a paper entitled Appropriate Recompense for Oocytes in Stem Cell Research presented at the Stem (...) class='Hi'>Cells: Hope or Hype debate, North West Genetics Knowledge Park, Manchester in May 2007.). (shrink)

In contrast to many countries, the political debates in the Netherlands on reproductive technologies and embryo research have paid particular attention to the issue of health risks to women. This article focuses on the question to what extent the discourse of gender has contributed to shaping the space for embryonic research in this country. The author argues that in the policy arena flexible conceptualizations of risks and burdens to women and of the identities of embryos have been crucial in drawing (...) and maintaining a discursive boundary between the domains of medically assisted reproduction and embryo research. The author shows that feminist intervention challenging this discursive strategy has had an impact on the present regulation of research. However, the main weakness of this temporary and partial feminist success is the virtual absence of a public debate on the meaning and desirability of embryo research. (shrink)

A large body of evidence on the activity of regulatory T (Treg) cells was gathered during the last decade, and a similar number of reviews and opinion papers attempted to integrate the experimental findings. The abundant literature clearly delineates an exciting area of research but also underlines some major controversies. A linear cause–result interpretation of experimental maneuvers often ignores the fact that the activity of Treg cells is orchestrated with the effector T (Teff) cells within an (...) intricate network of physiological immune homeostasis. Every modulation of the activity of the effector (cytotoxic) immune system revolves to affect the activity of regulatory (suppressive) cells through elaborate feedback loops of negative and positive regulation. The lack of IL‐2 production by innate Treg cells makes this cytokine a prime coupler of the effector and suppressive mechanisms. Here we attempt to integrate evidence that delineates the involvement of IL‐2 in primary and secondary feedback loops that regulate the activity of suppressive cells within the elaborate network of physiological immune homeostasis.©2007 Wiley Periodicals, Inc BioEssays 30:875–888, 2008. © 2008 Wiley Periodicals, Inc. (shrink)

This article highlights the current controversies around stem cell research and its application in clinical medicine. It aims to discuss the ethical concerns around how corporate involvement is corrupting the ethical progression in this field of research. The author appeals to medical and scientific communities to take cognisance of current practices and to facilitate the regulation of new stem cell therapies being advertised to the public.

This paper proposes a classification of hESC research regulation by shifting from the statutory content of relevant national Laws to the method of decision-making process, in order to verify whether it is possible to identify a connection between the concrete characters of that process and its outcome. A set of procedural indexes are identified and applied to the analysed legal systems. According to an increasing fulfilment of indexes, we may individuate two main regulatory families: the ‘value oriented’ and the (...) ‘procedure oriented’ ones. The latter is developing an increasing impact within European context: it is characterised by a mix of regulatory sources, each developing a specific function. Within this model, statutory law cannot infringe a regulatory space reserved to expertise and selfregulation, developing a subsidiary function; furthermore, it has to recognise the integrative role of expertise within statutory-making process. (shrink)

Transposable elements are no longer considered to be “junk” DNA. Here, we review how TEs can impact gene regulation systematically. TEs encode various regulatory elements that enables them to regulate gene expression. RJ Britten and EH Davidson hypothesized that TEs can integrate the function of various transcriptional regulators into gene regulatory networks. Uniquely TEs can deposit regulatory sites across the genome when they transpose, and thereby bring multiple genes under control of the same regulatory logic. Several (...) studies together have robustly established that TEs participate in embryonic development and oncogenesis. We discuss the regulatory characteristics of TEs in context of evolution to understand the extent of their impact on gene networks. Understanding these features of TEs is central to future investigations of TEs in cellular processes and phenotypic presentations, which are applicable to development and disease studies. We re-visit the Britten–Davidson “gene-battery” model and understand the genetic and transcriptional impact of TEs in innovating gene regulatory networks. Transposable elements are exogenous sequences that have either been co-opted or repurposed for host functions. The vast amounts of TE sequence in the genome provides raw material for gene expression regulation, and still remains to be fully understood; the “gene-battery” model provides the basis for understanding this. (shrink)

The stunning possibility of “reprogramming” differentiated somatic cells to express a pluripotent stem cell phenotype (iPS, induced pluripotent stem cell) and the “ground state” character of pluripotency reveal fundamental features of cell fate regulation that lie beyond existing paradigms. The rarity of reprogramming events appears to contradict the robustness with which the unfathomably complex phenotype of stem cells can reliably be generated. This apparent paradox, however, is naturally explained by the rugged “epigenetic landscape” with valleys representing “preprogrammed” attractor (...) states that emerge from the dynamical constraints of the gene regulatory network. This article provides a pedagogical primer to the fundamental principles of gene regulatory networks as integrated dynamic systems and reviews recent insights in gene expression noise and fate determination, thereby offering a formal framework that may help us to understand why cell fate reprogramming events are inherently rare and yet so robust. (shrink)

Stem cell tourism is a small but growing part of the thriving global medical tourism marketplace. Much stem cell research remains at the experimental stage, with clinical trials still uncommon. However, there are over 700 clinics estimated to be operating in mostly developing countries – from Costa Rica and Argentina to China, India and Russia – that have lured many patients, mostly from industrialized countries, driven by desperation and hope, which in turn continue to fuel the growth of such tourism.While (...) much research has focused on such dimensions as the promotions that allow such businesses to make their services known, media coverage, some patient research, and regulatory conditions for developing country clinics, little attention has been paid to the non-affected members of the general population, the future potential users of such services. This empirical study based on five focus group discussions with a diverse group of healthy adults in a Canadian city, explored participant views of patients who use stem cell tourism services, the likelihood they would avail themselves of such services if they were to suffer similar illnesses, and the conditions under which they might do so, and the impact that admonitions and advice from international expert bodies might have on their decisions. Our findings suggest that these healthy adults are sympathetic to the drivers of hope and desperation, and, despite cautions about research limitations, may seek such treatments themselves under similar conditions. These findings are discussed in the context of the policy and ethical issues raised by this form of medical tourism. (shrink)

Stem cell tourism is a small but growing part of the thriving global medical tourism marketplace. Much stem cell research remains at the experimental stage, with clinical trials still uncommon. However, there are over 700 clinics estimated to be operating in mostly developing countries – from Costa Rica and Argentina to China, India and Russia – that have lured many patients, mostly from industrialized countries, driven by desperation and hope, which in turn continue to fuel the growth of such tourism.While (...) much research has focused on such dimensions as the promotions that allow such businesses to make their services known, media coverage, some patient research, and regulatory conditions for developing country clinics, little attention has been paid to the non‐affected members of the general population, the future potential users of such services. This empirical study based on five focus group discussions with a diverse group of healthy adults in a Canadian city, explored participant views of patients who use stem cell tourism services, the likelihood they would avail themselves of such services if they were to suffer similar illnesses, and the conditions under which they might do so, and the impact that admonitions and advice from international expert bodies might have on their decisions. Our findings suggest that these healthy adults are sympathetic to the drivers of hope and desperation, and, despite cautions about research limitations, may seek such treatments themselves under similar conditions. These findings are discussed in the context of the policy and ethical issues raised by this form of medical tourism. (shrink)

Cell shape and cell contacts are determined by transmembrane receptor‐mediated associations of the cytoskeleton with specific extracellular matrix proteins and with ligands on the surface of adjacent cells. The cytoplasmic domains of these microfilament‐membrane associations at the adherens junction sites, also Iocalize a variety of regulatory molecules involved in signal transduction and gene regulation. The stimulation of cells with soluble polypeptide factors leads to rapid changes in cell shape and microfilament component organization. In addition, this stimulation also (...) activates the phosphoinositide signaling pathway. Recently, a linkage between actin‐binding proteins and the phosphoinositide signaling pathway, was discovered. It is Suggested that by the association with the second messenger system, and/or by controlling the localization of regulatory molecules, the cytoskeleton may regulate gene expression. (shrink)

Approaches to induce tumor differentiation often result in manageable and therapy‐naïve cellular states in cancer cells. This transformation is achieved by activating pathways that drive tumor cells away from plasticity, a state that commonly correlates with enhanced aggression, metastasis and resistance to therapy. Here, we discuss signaling pathways, epigenetics and non‐coding RNAs as three main regulatory levels with the potential to drive tumor differentiation and hence as potential targets in differentiation therapy approaches. The success of an effective (...) therapeutic regimen in one cancer, however, does not necessarily sustain across cancer types; a phenomenon largely resulting from heterogeneity in the genetic and physiological landscapes of tumor types necessitating an approach designed for each cancer's unique genetic and phenotypic build‐up. (shrink)

Clp ATPase chaperone proteins are found in procaryotes and eucaryotes. Recently, ClpC of Bacillus subtilis was found to be part of a regulatory switch(1). ClpC, in combination with the MecA and ComS proteins, regulates the activity of a transcription factor, ComK, which is necessary for the development of genetic competence (the ability to bind and take up exogenous DNA). The complex of ClpC:MecA:ComK renders ComK inactive. Interaction between ComS and the ternary complex releases active ComK. This regulatory switch (...) controls ComK activity in response to cell density signals that affect production of ComS. Regulated interaction between Clp ATPases and target proteins might prove to be widespread. (shrink)

In 1995, the eyeless (ey) gene was dubbed the “master‐regulator” of eye development in Drosophila. Not only is ey required for eye development, but its misexpression can convert many other tissues into eye, including legs, wings and antennae.(1) ey is remarkable for its ability to drive coordinate differentiation of the multiple cell types that have to differentiate in a very precise pattern to construct the fly eye, and for its power to override the previous differentiation programs of many other diverse (...) tissues. Even more remarkable, the ey homolog Pax6 and homologs of other eye determination genes from Drosophila are also required for eye development in vertebrates,(2,3) prompting reassessment of the evolution of vision throughout the animal kingdom.(4,5) Now Kumar and Moses have published a study that throws a new light on ey function in Drosophila.(6) According to their work, ey becomes a master regulator of eye development much later than previously thought, and is regulated by signalling through the Notch and EGFR signaling pathways. BioEssays 23:763–766, 2001. © 2001 John Wiley & Sons, Inc. (shrink)

Apical cells are universally present in lower plants and their description has been mostly viewed morphologically as single-celled meristems. This study attempts to demonstrate that the roles of apical cells and more generally of meristems collectively are (a) often the proliferative source of all cells in a plant, (b) sometimes a formative centre in histogenesis and organogenesis and (c) always a regulatory site. As a proliferative centre it occurs as a series of apical cells through (...) a mitotic lineage by unequal divisions which includes a rotational pattern to form cells distributed according to the symmetry of its organ. As a formative centre it determines leaf arrangement in mosses and leafy liverworts as well as the root cap and gametophyte cushion in ferns. It appears initially to determine the type of organ and later the organ determines the type of apical cells within. As a regulatory centre it activates distal secondary cells to proliferate as well as inhibiting neighbouring cells from becoming apical cells to preserve the identity of an organ during its development.Based on these three roles by which apical cells can be recognized an argument can be drafted that seed plants may have apical cells, although morphologically indistinguishable from other cells, singularly or in batteries instead of possessing the traditionally described multicellular meristems. (shrink)

The closely related debates concerning abortion, the protection of the embryo and stem cell science have captured the legislative agenda in Mexico in recent years. This paper examines some contemporary debates related to stem cell science and the legal and political action that has followed in the wake of the latest Supreme Court judgment on abortion, which debates are directly linked to the degrees of protection of the embryo stipulated in the Mexican Constitution. While some Mexican states have opted to (...) take no further action, others, where conservative political forces are in the majority, have been very active in seeking to ensure that their constitutions are amended to protect human life from conception onwards. This intense legislative activity has not, however, been repeated at the federal level, where there is currently no overarching national regulatory framework governing stem cell research. Although major efforts have been made by the conservative block within the Senate to bring forward legislative proposals for the prohibition of human embryonic stem cell research, and despite the public expression by the federal government of its commitment to encourage inward investment and innovation in the area of biotechnology, stem cell science has, so far, remained unregulated. The legislative challenge is to resist the pressure that has been injected by religious leaders and to act in accordance with the values and principles adopted by the community in the Mexican Constitution. In the final analysis, Mexico faces particular difficulties in accommodating conservative political forces on one hand, while recognising on the other its need, as an emerging economy, to promote a progressive approach to innovation in biotechnology. (shrink)

Two groups of plant viruses have DNA in their genomes. One group, the caulimoviruses, are non‐integrating retroviruses that package dsDNA in virions. The other group, the geminiviruses, package small circular ssDNA and include the only DNA viruses known with bipartite genomes. The regulation of transcription of these viruses is not well characterized, but recent work is beginning to yield interesting results. Regulatory sequences from these viruses function in cells of species that are not hosts of the virus and (...) are finding use in constitutive expression of chimeric genes in transformed plants. Development of vectors based on plant viruses requires further characterization at the molecular level of viral life cycles. (shrink)

Iron uptake and storage in mammalian cells is at least partly regulated at a posttranscriptional level by the iron regulatory proteins (IRP‐1 and IRP‐2). These cytoplasmic regulators share 79% similarity in protein sequence and bind tightly to conserved mRNA stem‐loops, named iron‐responsive elements (IREs). The IRP:IRE interaction underlies the regulation of translation and stability of several mRNAs central to iron metabolism. The question of why the cell requires two such closely related regulatory proteins may be resloved as (...) we learn more about the expression and regulation of these proteins. It is evident so far that, despite similarities, the IRPs differ in several important respects. They are coordinately regulated by cellular iron, but whereas IRP‐1 is inactivated by high iron levels, IRP‐2 is rapidly degraded. Further differences arise in their expression and RNA‐binding specificity. The two proteins each recognise a large repertoire of IRE‐like sequences, including a small group of exclusive RNA targets. These findings hint that IRP‐1 and IRP‐2 may bind preferenitially to certain mRNAs in vivo, possibly extending their known functions beyond the regulation of intracellular iron homeostasis. (shrink)

Recent years have witnessed an explosion of the single-cell biochemical toolbox including chromosome conformation capture -based methods that provide novel insights into chromatin spatial organization in individual cells. The observations made with these techniques revealed that topologically associating domains emerge from cell population averages and do not exist as static structures in individual cells. Stochastic nature of the genome folding is likely to be biologically relevant and may reflect the ability of chromatin fibers to adopt a number of (...) alternative configurations, some of which could be transiently stabilized and serve regulatory purposes. Single-cell Hi-C approaches provide an opportunity to analyze chromatin folding in rare cell types such as stem cells, tumor progenitors, oocytes, and totipotent cells, contributing to a deeper understanding of basic mechanisms in development and disease. Here, we review key findings of single-cell Hi-C and discuss possible biological reasons and consequences of the inferred dynamic chromatin spatial organization. Single-cell Hi-C expands the molecular biology toolbox for studies of chromatin structure in individual cells. This technique allows one to analyze cell-to-cell variability in TAD and loop structure, and to capture chromosome conformation in rare cell types such as oocytes, totipotent cells, and tumor progenitors. (shrink)

Recent years have witnessed an explosion of the single-cell biochemical toolbox including chromosome conformation capture -based methods that provide novel insights into chromatin spatial organization in individual cells. The observations made with these techniques revealed that topologically associating domains emerge from cell population averages and do not exist as static structures in individual cells. Stochastic nature of the genome folding is likely to be biologically relevant and may reflect the ability of chromatin fibers to adopt a number of (...) alternative configurations, some of which could be transiently stabilized and serve regulatory purposes. Single-cell Hi-C approaches provide an opportunity to analyze chromatin folding in rare cell types such as stem cells, tumor progenitors, oocytes, and totipotent cells, contributing to a deeper understanding of basic mechanisms in development and disease. Here, we review key findings of single-cell Hi-C and discuss possible biological reasons and consequences of the inferred dynamic chromatin spatial organization. Single-cell Hi-C expands the molecular biology toolbox for studies of chromatin structure in individual cells. This technique allows one to analyze cell-to-cell variability in TAD and loop structure, and to capture chromosome conformation in rare cell types such as oocytes, totipotent cells, and tumor progenitors. (shrink)

The paper looks in detail at patients that were treated at one of the most discussed companies operating in the field of untried stem cell treatments, Beike Biotech of Shenzhen, China. Our data show that patients who had been treated at Beike Biotech view themselves as proactively pursuing treatment choices that are not available in their home countries. These patients typically come from a broad variety of countries: China, the United Kingdom, the United States, South Africa and Australia. Among the (...) patients we interviewed there seemed to be both an awareness of the general risks involved in such experimental treatments and a readiness to accept those risks weighed against the possible benefits. We interpret this evidence as possibly reflecting the emergence of risk-taking patients as ‘consumers’ of medical options as well as the drive of patients to seek treatment options in the global arena, rather than being hindered by the ethical and regulatory constraints of their home countries. Further, we found that these patients tend to operate in more or less stable networks and groups in which they interact and cooperate closely and develop opinions and assessments of available treatment options for their ailments. These patients also perform a multiple role as patients, research subjects, and research funders because they are required to pay their way into treatment and research activities. This new social dynamics of patienthood has important implications for the ethical governance of stem cell treatments. (shrink)

The proteins encoded by the ras proto‐oncogenes play critical roles in normal cellular growth, differentiation and development in addition to their potential for malignant transformation. Several proteins that are involved in the control of the activity of p21ras have now been characterised. p120GAP stimulates the GTPase activity of p21ras and hence acts as a negative regulator of ras proteins. It may be controlled by tyrosine phosphorylation or association with tyrosine phosphorylated proteins. The neurofibromatosis type 1 (NF 1) gene also encodes (...) a potential GTPase activating protein which is likely to be subject to a different control mechanism. Guanosine nucleotide exchange factors for p21ras have now been identified: these may be positive regulators of ras protein function. It appears that p21ras is subject to rapid regulation by several distinct mechanisms which are likely to vary in different cell types; the ras proteins are thereby able to act as very sensitive cellular monitors of the extracellular environment. (shrink)

The generation of patterns and the diversity of cell types in a multicellular organism require differential gene regulation. At the heart of this process are enhancers or cis‐regulatory modules (CRMs), genomic regions that are bound by transcription factors (TFs) that control spatio‐temporal gene expression in developmental networks. To date, only a few CRMs have been studied in detail and the underlying cis‐regulatory code is not well understood. Here, we review recent progress on the genome‐wide identification of CRMs with (...) chromatin immunoprecipitation of TF‐DNA complexes followed by microarrays (ChIP‐on‐chip). We focus on two computational approaches that have succeeded in predicting the expression pattern driven by a CRM either based on TF binding site preferences and their expression levels, or quantitative analysis of CRM occupancy by key TFs. We also discuss the current limits of these methods and highlight some of the key problems that have to be solved to gain a more complete understanding of the structure and function of CRMs. (shrink)

Most of the essential cellular components, like nucleic acids, lipids and sugars, are phosphorylated. The phosphate equilibrium in Escherichia coli is regulated by the phosphate (Pi) input from the surrounding medium. Some 90 proteins are synthesized at an increased rate during Pi starvation and the global control of the cellular metabolism requires cross‐talk with other regulatory mechanisms. Since the Pi concentration is normally low in E. coli's natural habitat, these cells have devised a mechanism for synthesis of about (...) 15 proteins to accomplish two specific functions: transport of Pi and its intracellular regulation. The synthesis of these proteins is controlled by two genes (the phoB‐phoR operon), involving both negative and positive functions. PhoR protein is a histidine protein kinase, induced in Pi starvation and is a transmembrane protein. It phosphorylates the regulator protein PhoB which is also Pi starvation‐induced. The PhoB phosphorylated form binds specifically to a DNA sequence of 18 nucleotides (the pho Box), which is part of the promoters of the Pho genes. The genes controlled by phoB constitute the Pho regulon.The repression of phoA (the gene encoding alkaline phosphatase) by high Pi concentrations in the medium requires the presence of an intact Pst operon (pstS, pstC, pstA, pstB and phoU) and phoR. The products of pstA and pstC are membrane bound, whereas the product of pstS is periplasmic and PstB and PhoU proteins are cytoplasmic. The function of the PhoU protein may be regulated by cofactor nucleotides and may be involved in signaling the activation of the regulon via PhoR. (shrink)

The multistep pathway of eukaryotic gene expression involves a series of highly regulated events in the nucleus and cytoplasm. In the nucleus, genes are transcribed into pre‐messenger RNAs which undergo a series of nuclear processing steps. Mature mRNAs are then transported to the cytoplasm, where they are translated into protein and degraded at a rate dictated by transcript‐ and cell‐type‐specific cues. Until recently, these individual nuclear and cytoplasmic events were thought to be primarily regulated by different RNA‐ and DNA‐binding proteins (...) that are localized either only in the nucleus or only the cytoplasm. Here, we describe multifunctional proteins that control both nuclear and cytoplasmic steps of gene expression. One such class of multifunctional proteins (e.g., Bicoid and Y‐box proteins) regulates both transcription and translation whereas another class (e.g., Sex‐lethal) regulates both nuclear RNA processing and translation. Other events controlled by multifunctional proteins include assembly of spliceosome components, spliceosome recycling, RNA editing, cytoplasmic mRNA localization, and cytoplasmic RNA stability. The existence of multifunctional proteins may explain the paradoxical involvement of the nucleus in an RNA surveillance pathway (nonsense‐mediated decay) that detects cytoplasmic signals (premature termination codons). We speculate that shuttling multifunctional proteins serve to efficiently link RNA metabolism in the cytoplasmic and nuclear compartments. BioEssays 23:775–787, 2001. © 2001 John Wiley & Sons, Inc. (shrink)

During development one mechanism for generating different cell types is asymmetric cell division, by which a cell divides and contributes different factors to each of its daughter cells. Asymmetric cell division occurs through out the eukaryotic kingdom, from yeast to humans. Many asymmetric cell divisions occur in a defined orientation. This implies a cellular mechanism for sensing direction, which must ultimately lead to differences in gene expression between two daughter cells. In this review, we describe two classes of (...) molecules: regulatory factors that are differentially expressed upon asymmetric cell division, and components of a signal transduction pathway that may define cell polarity. The lin‐11 and mec‐3 genes of C. elegans, the Isl‐1 gene of mammals and the HO gene of yeast, encode regulatory factors that determine cell type of one daughter after asymmetric cell division. The CDC24 and CDC42 genes of yeast affect both bud positioning and orientation of mating projections, and thus may define a general cellular polarity. We speculate that molecules such as Cdc24 and Cdc42 may regulate expression of genes such as lin‐11, mec‐3, Isl‐1 and HO upon asymmetric cell division. (shrink)

The cell division and differentiation events that occur during the development of the nematode Caenorhabditis elegans are nearly identical between different individuals, a feature that distinguishes this organism from larger and more complex metazoans, such as humans and Drosophila. In view of this discrepancy, it might be expected that the regulation of cell growth, division and differentiation in C. elegans would involve mechanisms separate from those utilized in larger animals. However, the results of recent genetic, molecular and cellular studies indicate (...) that C. elegans employs an arsenal of developmental regulatory mechanisms quite similar to those wielded by its arthropod and vertebrate relatives. Thus, the nematode system is providing both novel and complementary insights into the general problem of how growth and patterning events are integrated in development. This review offers a general perspective on the regulation of cell division and growth in C. elegans, emphasizing recent studies of these crucial aspects of development. BioEssays 24:38–53, 2002. © 2002 John Wiley & Sons, Inc. (shrink)

Endothelial cells line the inside of all blood vessels, forming a structurally and functionally heterogenous population of cells. Their complexity and diversity has long been recognized, yet very little is known about the molecules and regulatory mechanisms that mediate the heterogeneity of different endothelial cell populations. The constitutive organ‐ and microenvironment‐specific phenotype of endothelial cells controls internal body compartmentation, regulating the trafficking of circulating cells to distinct vascular beds. In contrast, surface molecules associated with the (...) activated cytokine‐inducible endothelial phenotype play a critical role in pathological conditions including inflammation, tumor angiogenesis, and wound healing. Differentiation of the endothelial cell phenotypes appears to follow similar mechanisms to the differentiation of hematopoietic cells, with the exception that endothelial cells maintain transdifferentiating competence. The present review offers a scheme of endothelial cell differentially expressed endothelial cell molecules as targets for directed therapeutic intervention. (shrink)

Ribosomal RNA transcription was one of the first model systems for molecular characterization of a transcription regulatory mechanism and certainly one of the best studied in the widest range of organisms. In multicellular organisms, however, the issue of cell‐type‐specific regulation of rRNA transcription has not been well addressed. Here I propose that a systematic study of cell‐type‐specific regulation of rRNA transcription may reveal new regulatory mechanisms that have not been previously realized. Specifically, issues concerning the cell‐type‐specific requirement for (...) rRNA production, the universality of Pol I transcription complex and the division of rDNA into regulatory subdomains are discussed. BioEssays 28: 719–725, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

Langerhans cells (LCs), residing in the epidermis, are able to induce potent immunogenic responses and also to mediate immune tolerance. We propose that tolerogenic and immunogenic responses of LCs are directed by signaling from the epidermis and involve counter‐acting gene circuits that are coupled to a core maturation gene module. We base our analysis on recent genetic and genomic findings facilitating the understanding of the molecular mechanisms controlling these divergent immune functions. Comparing gene regulatory network (GRN) analyses of (...) various types of dendritic cells (DCs) including LCs we integrate signaling‐dependent (TGFβ, EpCAM, β‐Catenin) and transcription factor (IRF4, IRF1, NFκB) regulated gene circuits that appear to orchestrate the distinctive LC functional states. Our model proposes, that while epidermal signaling in the steady‐state promotes LC tolerogenic function, the disruption of cell‐cell contacts coupled with inflammatory signaling induces LC immunogenic programing. The conceptual framework emphasizes the sensing of discrete epidermal and inflammatory cues by resident LCs in dictating their genomic programing and cell state dynamics. (shrink)

Neddylation, a ubiquitylation‐like post‐translational modification, is catalyzed by a cascade composed of three enzymes: E1 activating enzyme, E2 conjugating enzyme, and E3 ligase with cullins as physiological substrates. Specifically, neddylation E2 UBE2M couples with E3 RBX1 to neddylate cullins 1–4, whereas neddylation E2 UBE2F couples with E3 RBX2/SAG to neddylate cullin 5, leading to activation of CRL1‐4 (Cullin‐RING ligases 1–4) and CRL5, respectively. While over‐activation of the neddylation‐CRLs axis occurs frequently in many human cancers, how neddylation‐CRLs regulate the function of (...) immune cells, particularly Treg cells was previously unknown. To this end, we recently performed Treg selective knockout of two neddylation E2s and two E3s, individually, driven by Foxp3‐Cre, and found that while the Ube2f‐Sag E2/E3 pair plays a minimal role, if any, the Ube2m‐Rbx1 pair is essential for the maintenance of Treg functionality, since their deletion triggers robust inflammatory response with autoimmune phenotypes. Milder phenotype severity upon Treg KO of upstream Ube2m than that of downstream Rbx1 strongly suggested that Rbx1 regulates Treg function in a manner dependent and independent of neddylation. (shrink)

In the biomedical field, calls for the generation of new regulations or for the amendment of existing regulations often follow the emergence of apparently new research practices (such as embryonic stem cell research), clinical practices (such as facial transplantation) and entities (such as Avian Influenza/’Bird Flu’). Calls for regulatory responses also arise as a result of controversies which bring to light longstanding practices, such as the call for increased regulation of human tissue collections that followed the discovery of unauthorised (...) post-mortem organ retention. Whilst it seems obvious that new regulations should only be generated if existing regulations are inadequate (a practice referred to in this paper as ‘regulatory syncretism’), this does not always occur in practice. This paper examines the conceptual steps involved in generating regulatory responses to emerging phenomena. Two decision points are identified. First, a stance is taken as to whether the emerging phenomenon raises unique ethical or legal issues (exceptionalism versus non-exceptionalism). Second, the decision is made as to whether new regulation should be generated only for truly unique phenomena (syncretism versus asyncretism). It is argued here that it is important to make a careful assessment of novelty, followed by a reflective and deliberate choice of regulatory syncretism or asyncretism, since each type of regulatory response has advantages which need to be harnessed and disadvantages which need to be managed—something that can only occur if regulators are attentive to the choices they are making. (shrink)

Stem cell technology is an emerging science field; it is the unique regenerative ability of the pluripotent stem cell which scientists hope would be effective in treating various medical conditions. While it has gained significant advances in research, it is a sensitive subject involving human embryo destruction and human experimentation, which compel governments worldwide to ensure that the related procedures and experiments are conducted ethically. Based on face-to-face interviews with selected Malaysian ethicists, scientists and policymakers, the objectives and effectiveness of (...) the current Guideline for Stem Cell Research and Therapy are examined. The study’s findings show that the guideline is rather ineffective in ensuring good ethical governance of the technology. A greater extent of unethical conduct is likely present in the private medical clinics or laboratories offering stem cell therapies compared with the public medical institutions providing similar services, as the latter are closely monitored by the governmental agencies enforcing the relevant policies and laws. To address concerns over malpractices or unethical conduct, this paper recommends a comprehensive revision of the current stem cell guideline so that adequate provisions exist to regulate the explicit practices of the private and public stem cell sectors, including false advertising and accountability. The newly revised Malaysian stem cell guideline will align with the Guidelines for Stem Cell Research and Clinical Translation of the International Society for Stem Cell Research containing secular but universal moral rules. However, a regulatory policy formulated to govern the technology remains the main thrust of empowering the guideline for compliance among the stakeholders. (shrink)

Transcriptional networks regulate cell fate decisions, which occur at the level of individual cells. However, much of what we know about their structure and function comes from studies averaging measurements over large populations of cells, many of which are functionally heterogeneous. Such studies conceal the variability between cells and so prevent us from determining the nature of heterogeneity at the molecular level. In recent years, many protocols and platforms have been developed that allow the high throughput analysis (...) of gene expression in single cells, opening the door to a new era of biology. Here, we discuss the need for single cell gene expression analysis to gain deeper insights into the transcriptional control of cell fate decisions, and consider the insights it has provided so far into transcriptional regulatory networks in development. (shrink)

Evolution has shaped all living organisms on Earth, although many details of this process are shrouded in time. However, it is possible to see, with one's own eyes, evolution as it happens by performing experiments in defined laboratory conditions with microbes that have suitably fast generations. The longest‐running microbial evolution experiment was started in 1988, at which time twelve populations were founded by the same strain ofEscherichia coli. Since then, the populations have been serially propagated and have evolved for tens (...) of thousands of generations in the same environment. The populations show numerous parallel phenotypic changes, and such parallelism is a hallmark of adaptive evolution. Many genetic targets of natural selection have been identified, revealing a high level of genetic parallelism as well. Beneficial mutations affect all levels of gene regulation in the cells including individual genes and operons all the way to global regulatory networks. Of particular interest, two highly interconnected networks—governing DNA superhelicity and the stringent response—have been demonstrated to be deeply involved in the phenotypic and genetic adaptation of these experimental populations. BioEssays 29:846–860, 2007. © 2007 Wiley Periodicals, Inc. (shrink)

Of the many proposals for inferring genetic regulatory structure from microarray measurements of mRNA transcript hybridization, several aim to estimate regulatory structure from the associations of gene expression levels measured in repeated samples. The repeated samples may be from a single experimental condition, or from several distinct experimental conditions; they may be “equilibrium” measurements or time series; the associations may be estimated by correlation coefficients or by conditional frequencies (for discretized measurements) or by some other statistic. This paper (...) describes two elementary statistical difficulties for all such procedures, no matter whether based on Bayesian updating, conditional independence testing, or other machine learning procedures such as simulated annealing or neural net pruning. One difficulty obtains if large numbers of cells are aggregated in a measurement of expression levels from a common population of cells; the other obtains if small numbers of cells are aggregated or if samples are separately aggregated over different populations of cells. (shrink)

The ability to memorize changes in the environment is present at all biological levels, from social groups and individuals, down to single cells. Trans‐generational memory is embedded subcellularly through genetic and epigenetic mechanisms. Evidence that cells process and remember features of the immediate environment using protein sensors is reviewed. It is argued that this mnemonic ability is encapsulated within the protein conformational space and lasts throughout its lifetime, which can overlap with the lifespan of the organism. Means to (...) determine diachronic changes in protein activity are presented. (shrink)